Kim Newsome, M.P.H., from the U.S. Centers for Disease Control and Prevention in Atlanta, and colleagues collected data on outcomes of infants born to pregnant women with 2009 H1N1 influenza. Information on pregnant women with confirmed H1N1 influenza was linked to their infants’ birth certificates. Birth certificate data were also collected from two comparison groups. Data were included for 490 pregnant women with influenza and for 1,451 and 1,446 pregnant women without reported influenza with pregnancies in the same year and with prior-year pregnancies, respectively.

The researchers found that relative to the comparison groups, women with 2009 H1N1 influenza admitted to an ICU (64 women) were more likely to deliver preterm infants, low birth-weight infants, and infants with Apgar scores ≤6 at five minutes (for same-year comparison, adjusted relative risks, 3.9, 4.6, and 8.7, respectively). No significantly elevated risks for adverse outcomes were seen for women with influenza who were not hospitalized and for hospitalized women not admitted to the ICU.

“More research is needed to further understand the nuances of infant risks among pregnancies with seasonal influenza virus infection, but these current findings provide important additional evidence of influenza risk during pregnancy,” the authors write.